Human Brains Aren't Distinctly Male or Female, Study Says

Instead, researchers find 'mosaic' of masculine, feminine traits.

By Randy Dotinga, HealthDay News

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The findings suggest people shouldn't be treated differently based on their sex, researchers noted.

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There's no such thing as a distinctly male or female brain, new research suggests.

An analysis of more than 1,400 MRI scans suggests that biologically unmistakable sex differences don't extend to the brain. Instead, the brain is home to a mix of masculine and feminine characteristics, the researchers found.

"This is the first study to look at the brain as a whole and ask whether brains are of two types. The answer is no," said study lead author Daphna Joel, a psychologist and professor at Tel-Aviv University in Israel.

"Each person possesses a unique mosaic of characteristics: some more common in females compared to males, some more common in males compared to females, and some common in both," Joel said.

The question has been debated throughout the ages: Are human brains as gender-specific as chromosomes and sexual organs are in most people? Or are things more complicated?

To gain more insight, Joel and colleagues analyzed MRI brain scans of 1,400 people. They found that the brains of males and females tended not to stand apart in terms of gray matter, white matter and connections inside the brain. (Gray matter refers to brain cells known as neurons; white matter connects neurons to each other.)

The findings revealed that "many more brains" included both traits that are more common in females and traits more common in men, Joel said.

The researchers also analyzed three previous studies of personality traits, actions and attitudes involving more than 5,500 people. Again, they found that it's rare for people to be consistently masculine or feminine in the way they act. Instead, people tend to have a mix of male and female traits.

Still, Joel said the new study doesn't address how your actions reflect your gender. "We did not deal at all with the questions where differences in brain and behavior come from -- nature or nurture -- nor did we attempt to link differences in brain structure to differences in behavior," she said.

However, the findings suggest people shouldn't be treated differently based on their sex, she said.

"For example, single-sex education is often advocated on the basis of the claim that such schools can specifically cater to 'boy brains' and 'girl brains,'" she said.

"Our results undermine the entire concept of boy/girl brains. Who has a boy brain? The few boys who are consistently at the male end?" Joel said. "And if these boys have a 'boy brain' then what type of brain do the other boys have?"

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In general, she added, any argument "that builds on the assumption that girls' brains are like this and boys' brains are like that -- or that girls are like this and boys are like that -- is in trouble."

Dr. Meng-Chuan Lai, an assistant professor of psychiatry at the University of Toronto, agreed.

"Over the decades, scientists have already learned that most features of the brain and mind between male and female animals, including humans, are not categorically distinct," Lai said. It's akin to body height in humans, she said. "On average, males are taller, but there are many female individuals who are taller than male individuals."

How does this new research fit in? "This paper strengthens this common scientific view," said Lai, who wasn't involved in the study.

The study is published in the Nov. 30 issue of the Proceedings of the National Academy of Sciences.